A sewing machine for seaming together edges of web fabric workpieces normally has a large feed table surrounding the machine sewing head and serving to support the goods in front of, behind, and to the side of the sewing head relative to the travel direction of the goods through the head. In addition there is immediately upstream of the sewing head an edge guide comprised of three plates forming two laterally open superposed slots. The workpieces are superposed and the edges of the upper and lower workpieces are fitted respectively to the upper and lower slots and the operator guides the two workpieces through the slots to the sewing head aligned in the travel direction behind them.
This style of operation has many problems. The slot width must be carefully adjusted if the plates are fixed to prevent the workpieces from folding over at the edges, or the spring force must be perfectly set if the plates are biased together to prevent the goods from snagging.
In an advanced system such as described in West German Pat. Nos. 2,758,262 and 2,839,399, the upper and lower plates have angled nozzles from which air jets are emitted to press the workpieces against the upper and lower faces of the middle plate. Even in this arrangement the guide presents considerable drag to the workpieces so that feeding to the sewing station is a laborious and relatively slow process which can scarcely be tolerated in the effeciency-conscious garment industry. Furthermore, thick goods are subjected to greater lateral force than thin goods, so that feed problems are in part a function of the thickness of the fabric being guided and worked on. Finally in such a system the horizontal component of force exerted on the workpieces to hold them in the guide slots is small compared to the friction force against the table, so that these angled jets serve more a purpose of holding the workpiece edges on the middle plate than urging these edges horizontally all the way into the respective guide slots.
In addition the feed table itself poses quite some drag to the goods as the large contact area between it and the lower face of the lower workpiece has considerable static friction, since the workpieces are not displaced rapidly enough to overcome static friction. Attempts to provide air cushions to float the workpieces have proven unworkable due to the low mass/area ratio of the workpieces. Vibrating-table arrangements such as used in bulk particulate conveyors have also been found unworkable as the surface texture of many fabric workpieces is sufficient that this structure can flex to follow the microscopic reciprocations of the table, thereby rendering the system completely nonfunctional.